1. Field of the Invention
The present invention relates to an optical disk drive and, more particularly, to a controller for the optical disk drive and a semiconductor integrated circuit monolithically integrating the controller on a single semiconductor chip.
2. Description of the Related Art
A compact disk-recordable/rewritable (CD-R/RW) device is available as a recordable optical disk. Moreover, digital versatile disk-recordable/rewritable (DVD-RW) and digital versatile disk+recordable/rewritable (DVD+RW) devices are available as optical disks, which have a large-capacity compared to the CD-R/RW. In recording, “additional write”, i.e., writing new data which includes previously recorded data on the optical disk is offer necessary. A standard has been established such that an end of the previously recorded data and an initial point of new data coincide with each other within an accuracy of ±1 byte.
In order to permit the additional write in accordance with the standard, a method of recording new data on the optical disk by use of an information signal as a reference has been proposed (hereinafter referred to as “first background art”). The information signal is obtained from the optical disk. Also, a method of recording new data on the optical disk based on a wobble clock obtained by multiplying a wobble signal has been proposed (hereinafter referred to as “second background art”).
In the first background art, when the previously recorded data on the optical disk deviates from the standards, the new data deviates from the prepits and a wobble. Furthermore, in a digital versatile disk (DVD) drive and the like, a track pitch is narrower than the size of a beam spot. As a result, crosstalk often occurs between tracks. Under the influence of the wobble of adjacent tracks on the optical disk, the wobble signal is subjected to an amplitude modulation (AM) and a frequency modulation (FM). When the wobble signal undergoes the AM and the FM modulation, an error occurs in the wobble clock.
Therefore, according to the second background art, it is difficult to maintain phases of the record sync and prepits constantly, by use of the wobble clock as the reference. Furthermore, when the previously recorded data on the optical disk deviates from the standard, new data is recorded in accordance with prepits and the wobble, while ignoring the deviating data. If the new data is recorded while ignoring the previously recorded deviation data, there is a possibility that the previously recorded data will be destroyed.